This invention relates to a printing head for a printing machine. It is common knowledge that plastics materials can have printed matter, decorations or the like applied thereto by the transfer of dye from a carrier foil by heat and pressure. A basic hot stamping machine able to carry out this process consists of a press with a heated flat plate attached to a ram to which the respective embossed die or typeface is fastened. The article to be printed is placed on a holder with the carrier foil placed between the die and article. Pressure is obtained by interaction between the die and holder.
The greatest problem with this type of printing machine resides in the changing of typeface as this is intricate and time consuming. The problem is compounded when, for example, consecutive numbering is being carried out. To overcome this problem a device has been devised which includes numbering wheels otherwise known as an "odometer". The odometer is heated by an electric cartridge element which is located inside the shaft around which the wheels revolve. The odometer has not been entirely satisfactory as the upper half of the wheels receive more heat if kept stationary for a prolonged period.
In consecutive numbering with three or more digits the units and tens revolve around the heater element at reasonably constant intervals thereby equalising the temperature differences in the wheels, but the hundred or thousands are stationary for a prolonged time and lose their heat by virtue of absorption into the material being printed and general heat loss. As a certain quantity and evenness of heat is required to give a good impression and transfer of dye into a plastic article, an inferior imprint relative to the other (units and tens) numerals results. For quality control this is undesirable and in some cases not acceptable.
One aim of the invention is to provide a magazine type printing head for a printing machine which has the facility of speedy selection of different typeface.
A further aim of the invention is to provide a printing head for a hot stamping machine which gives a constant and uniform level of heat over the typeface being used as well as those stored in the head.